Process for the production of a stain-resistant photographic silver halide emulsion

ABSTRACT

The stability of silver halide emulsion layers against the deleterious effect of dust in particular metal dust is improved by adding to the physically ripened and washed emulsion before chemical ripening a silver chloride emulsion or by precipitating silver chloride on to the physically ripened and washed silver halide emulsion.

United States Patent [191 Hammerstein et al.

[ Apr. 16, 1974 PROCESS FOR THE PRODUCTION OF A STAIN-RESISTANTPHOTOGRAPHIC SILVER HALIDE EMULSION Inventors: Hanns Hammerstein,Hamburg;

Helmut Reuss, Leverkusen; Erik Moisar, Cologne, all of Germany Assignee:Agfa-Gevaert Aktiengesellschaft,

Leverkusen, Germany Filed: Sept. 5, 1972 Appl. No.: 286,291

Foreign Application Priority Data Sept. 3, 1971 Germany 2144127 US. Cl.96/94 R, 96/110 Int. Cl G03c 1/02, G036 l/72 Field of Search 96/1 10, 94

References Cited UNITED STATES PATENTS 3,600,180 8/1971 Judd et al.96/94 R Primary Examiner-Norman G. Torchin Assistant ExaminerAlfonso T,Suro Pico Attorney, Agent, or Firm-Connolly and Hutz [57] ABSTRACT 3Claims, No Drawings PROCESS FOR THE PRODUCTION OF A STAIN-RESISTANTPHOTOGRAPHIC SILVER HALIDE EMULSION The invention relates to a methodfor decreasing the formation of small stains caused by the presence ofheavy metals and/or their compounds or other contaminating substances inphotographic silver halide emulsions, auxiliary layers and supports forphotographic silver halide emulsions.

It is known that cleanliness is extremely important in the manufactureof light-sensitive photographic materials. Photographically active dustsuch as abrasion dust from metal contaminates the light-sensitive silverhalide emulsion layer in spite of all precautions. The metal particlesor their compounds or other photographically active substances dissolvein the photographic layers, auxiliary layers or supports with varyingdegrees of rapidity. The dissolved products diffuse in the layers andare liable to cause considerable harm to the photographic properties,e.g. by exerting a sensitizing or desensitizing effect. The well-knownblack or white patchiness is then found in the light-sensitivephotographic materials after they have been processed in photographicbaths in the usual manner.

A similar harmful effect may also be caused by impurities e.g. in theraw material used for the production of the paper support. In that case,black or white patchiness is found in the material after development,especially if the material is stored under conditions of elevatedtemperature and moisture.

Various additives have been described for preventing this effect. Theseadditives areincorporated either in the emulsion or in adjacent layers.Most of these substances, however, produce only a slight effect whilstothers become sufficiently effective only at high concentrations atwhich they often give rise to other harmful side effects.

It is an object of this invention to modify the process for producingthe photographic silver halide emulsion so that patchiness due to thepresence of dust and heavy metal particles will not occur.

A process for the production of a photographic silver halide emulsioncomprising the steps of precipitation of the silver halide in thepresence of a protective colloid, physical ripening, washing of theripened emulsion to remove the soluble salts and chemical ripening hasnow been found in which a gelatin emulsion containing essentially onlysilver chloride is added to the physically ripened and washed emulsionbefore it is chemically ripened, or the silver chloride which is to beadded is produced in the physically ripened and washed silver halideemulsion by precipitation by the addition of alkali metal chloride andsilver nitrate solutions.

The method according to the invention results in the formation of silverchloride hillocks on the silver halide grains of the original emulsion.These hillocks surprisingly produce excellent resistance to theformation of stains by particles of dirt. These silver chloride hillockson the particles of the original silver halide emulsions, which ispreferably a silver bromide emulsion, are clearly visible under anelectron microscope.

The concentration of silver chloride produced in the original silverhalide emulsion either by the addition of a silver chloride emulsion orby precipitation may vary within wide limits. The optimum quantity canbe determined by tests well known in the art. Quantities of from 2 to 10mol of silver chloride, based on the total quantity of silver halide inthe physically ripened and washed emulsion have generally been found toeffect sufficient stabilization for practical purposes.

It is preferable to use an excess of chloride ions for producing thesilver chloride hillocks. This excess should preferably be from 1.2 to 2times to required equimolar quantity of chloride ions. The production ofsilver halide emulsions modified in accordance with the invention isotherwise carried out by the usual process which comprises the followingsteps:

1. Precipitation of the silver halides in the presence of a protectivecolloid and physical ripening;

2. Removal of the excess water-soluble salts formed in the process ofprecipitation by washing the ripened emulsion; and

3. Chemical ripening of the washed emulsion to provide the desiredphotographic properties, in particular the desired sensitivity.

The silver halides used for the emulsion which is to be stabilized maybe silver chloride, silver bromide or mixtures of these if derived witha silver iodide content of up to 10 The silver halides are dispersed inthe usual hydrophilic binders, e.g. in proteins, preferably gelatin,carboxyrnethyl-cellulose, polyvinyl alcohol, polyvinyl pyrrolidone oralginic acid and its derivatives such as salts, esters or amides.

After the treatment with silver chloride in accordance with theinvention, the emulsions may be chemically ripened in the usual mannerand treated with the usual additives. The emulsion may be opticallysensitized with cyanines rhodacyanines or merocyanines, e.g. asdescribed in The Cyanine Dyes and related Compounds by F. M. HAMER,published by Intersci-' ence Publishers (1964). i

The emulsions may be chemically sensitized in the usual manner, e.g.with reducing agents such as tin(ll) salts, polyamines such asdiethyltriamine or sulfur compounds as described in U.S. Pat.specification No. 1,574,944. Salts of noble metals such as ruthenium,rhodium, palladium, iridium, platinum or gold may also be added aschemical sensitizers, as described in the publication by R. KOSLOWSKY inZ. Wiss. Phot. 46, 65 72 (1951). The emulsions may also containpolyalkylene oxides as chemical sensitizers and in particularpolyethylene oxides and derivatives thereof.

The emulsions may be stabilized against spontaneous fogging by theaddition of the usual stabilizers such as organic mercury compounds ormercury salts, e.g. mercury triazole compounds, simple mercury salts ormercury double salts. Other useful stabilizers are in particularazaindenes, e.g. tetraor pentaazaindenes and particularly those whichare hydr 'oxyl substituted or amino substituted, as described in thepublication by BIRR in Z. Wiss. Phot. 47, 2 58 (1952). Heterocyclicmercapto compounds such as l-phenyl-S-mercaptotetrazole, quaternarybenzothiazole derivatives and benzotriazoles may also be used.

The emulsion is hardened in the usual manner, e.g. with aldehydes suchas formaldehyde, dialdehydes or halo substituted aldehydes which containa carboxyl group, e.g. mucochloric acid or mucobromic acid, or diketonesor sulfonic acid esters such as methanesulfonic acid esters.

The emulsions prepared in accordance with the invention may be used forvarious photographic materials. They are particularly suitable forsilver halide emulsion layers used for photographic copying materialsmounted on a paper support but they may also be used for X-ray films,unsensitized emulsions, orthochromatically or panchromaticallysensitized emulsions or emulsions which are sensitive to the infra-redregion of the spectrum. The emulsions may be used in materials for thesilver saltdiffusion process, in color photographic materials and alsoin photographic materials for the silver dye bleaching process.

EXAMPLE 1 A silver bromide emulsion containing 14 mols of silverchloride and 1 mol of silver iodide is prepared in the usual manner byprecipitation in the presence of gelatin.

The emulsion is flocculated after physical ripening and the solublesalts resulting from precipitation are removed by washing with water.The silver halide is then melted at pH 5.5 with the addition of gelatinand water. The emulsion then contains 55 g of silver halide per kg and220 g of gelatin per kg. It is then ripened to the required sensitivityat 53 C.

In addition, the following additives are introduced into the castingsolution:

10 ml of a 0.1 aqueous solution of optical sensitizer of the followingformula:

10 ml of a l aqueous solution of a 2-mercapto-4-keto-3,4-dihydro-pyrimidine of the following formula as stabilizer:

20 ml ofa 5 aqueous solution of saponin and 0.75 ml of a 30 aqueoussolution of formaldehyde.

The emulsion is applied to a baryta-coated paper support to which alayer of gelatin containing iron dust has been applied to test theeffectiveness of the process according to the invention.

The emulsion is uniformly exposed and developed in a developer of thefollowing composition:

p-methylaminophenol Na,SO, sicc. l hydroquinone soda sicc. 2

per litre of water The sample obtained after processing is uniformlyblack. It has numerous white patches which can be attributed to theharmful effect of the iron dust.

In another test, an emulsion is prepared by the same method except that,after washing and before chemical ripening, 20 ml of a aqueous sodiumchloride solution and 83 ml ofa 5 aqueous silver nitrate solution areadded. When precipitation takes place, hillocks of silver chloride areformed on the grains of the original emulsion. The quantity of silverchloride produced by precipitation is 8.3 mols of silver chloride basedon the amount of silver halide in the original emulsion. The emulsion isthen chemically ripened and processed as described above.

The developed and fixed sample is practically free from stains. In thecase of the emulsion prepared according to the invention, practically nowhite stains are formed even if the sample has been stored in an airconditioning cupboard at C and 40 atmospheric humidity for 2 days beforeprocessing. In the comparison emulsion the formation of stains isincreased under these conditions.

EXAMPLE 2 A silver bromide emulsion containing 4.8 mols of silverchloride and 1.5 mols of silver iodide is prepared in the usual mannerby precipitation in the presence of gelatin as protective colloid.

It is physically ripened and the emulsion is flocculated and the solublesalts are removed by washing. The silver halide is then redispersed bythe addition of gelatin and water at pH 5.5. The emulsion then contains55 g of silver halide and 160 g of gelatin per kg.

The emulsion is then divided into two portions. 4 ml of a 10 sodiumchloride solution and 17 ml of a 5 aqueous silver nitrate solution areadded to one portion. The quantity of silver chloride produced, whichforms hillocks on the grains of the original silver bromide emulsion, is1.7 mols based on the amount of original emulsion.

Both portions are then chemically sensitized to the required sensitivityunder the same conditions at 49 C. Saponin and formaldehyde are thenadded as in Example l and in addition 5.3 ml of a l methanolic solutionof l-phenyl-5-mcrcaptotetrazole as stabilizer.

The material is processed in the same way as de scribed in Example 1.

Examination of the resulting sample shows that the formation of whitestains has again been practically completely suppressed by the processaccording to the invention while the comparison sample has numerouswhite stains.

EXAMPLE 3 The procedure is the same as that described in Example l, butinstead of adding sodium chloride solution and silver nitrate solutionto the physically ripened and washed emulsion, a previously preparedsilver chloride gelatin emulsion is added.

The subsequent treatment is the same as described in Example 1.Examination of the sample shows equally good results to those obtainedin Example I.

Equally effective stabilization and prevention of the formation of whitestains is achieved if instead of the 6 times the equimolar quantity ofchloride ions is present when the silver chloride emulsion is added orthe silver chloride is formed by precipitation.

3. The process of claim 1, wherein the amount of Si]- ver chlorideintroduced by the addition of silver chloride or by precipitation in thewashed emulsion is from 2 to 10 mols based on the silver halide of theoriginal silver halide emulsion.

2. The process of claim 1, wherein from 1.2 to 2 times the equimolarquantity of chloride ions is present when the silver chloride emulsionis added or the silver chloride is formed by precipitation.
 3. Theprocess of claim 1, wherein the amount of silver chloride introduced bythe addition of silver chloride or by precipitation in the washedemulsion is from 2 to 10 mols %, based on the silver halide of theoriginal silver halide emulsion.